**9.100 Figure P9.100 shows a modified cascode differential amplifier. Here Q3 and Q4 are the cascode transistors. However, the manner in which Q3 is connected with its base current feeding the current mirror Q7–Q8 results in very interesting input properties. Note that for simplicity the circuit is shown with the base of Q2 grounded. Assume that all transistors have equal β’s.(a) With vI =0 V dc, find the input bias current IB assuming all transistors have equal value of β. Compare with the case without the Q7–Q8 connection.(b) With vI =0 V (dc) + vid, find the input signal current ii and hence the input differential resistance Rid. Compare with the case without the Q7–Q8 connection. By what factor does R id increase?

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images - **9.100 Figure P9.100 shows a modified cascode differential amplifier. Here Q3 and Q4 are the cascode transistors. However, the manner in which Q3 is connected with its base current feeding the current mirror Q7–Q8 results in very interesting input properties. Note that for simplicity the circuit is shown with the base of Q2 grounded. Assume that all transistors have equal β’s.(a) With vI =0 V dc, find the input bias current IB assuming all transistors have equal value of β. Compare with the case without the Q7–Q8 connection.(b) With vI =0 V (dc) + vid, find the input signal current ii and hence the input differential resistance Rid. Compare with the case without the Q7–Q8 connection. By what factor does R id increase?

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